Project summary/ Abstract: The main goal of my proposal is uncover avenues that modulate BMPRII signaling. This signaling pathway is relevant in pulmonary arterial hypertension (PAH), a disease leading if untreated, to right heart failure and death. 70% of patients with familial and 20% of patients with idiopathic (I-) PAH carry a mutation in the bone morphogenetic protein receptor (BMPR)-II. However, the penetrance to develop PAH is less than 20%. Recent studies have shown that reduced levels of the wild-type BMPRII allele discriminate between affected and non- affected family members. Even PAH associated with other diseases (APAH) can be accompanied by reduced protein expression of BMPRII. Downregulation of BMPRII protein, but not mRNA, has been described in some IPAH patients, suggesting a post-transcriptional mechanism of regulation and this may also be true for the many IPAH patients without mutations. Therefore a novel approach that might ultimately lead to the prevention and treatment of pulmonary hypertension could be restoration of BMPRII signaling. Micro RNAs are involved in posttranscriptional regulation of gene expression, and microRNA 21 (miR-21) in particular can target BMPRII mRNA. In Specific Aim 1 we will use miR-21 mimics and antagomirs to modulate the levels of miR-21 and BMPRII in human pulmonary artery endothelial cells (PAECS) and smooth muscle cells (PASMCs) as well as in cells isolated from a mouse with reduced BMPRII levels. In addition we will confirm that BMP signaling and function in response to BMPs are restored by increasing BMPRII. Specific Aim 2 is to pursue a second very promising avenue to increase BMP signaling by screening for pharmacologically active compounds that could enhance signaling via BMPRII. We will develop a High Throughput Screen (HTS) using 3,600 FDA approved pharmacologically active compounds. In addition to hits that enhance BMP signaling, we will identify molecules that inhibit signaling through the BMPRII receptor and could therefore be harmful in IPAH patients and non-affected family members with compromised BMPRII expression. We will again verify that BMP signaling and function in response to BMP will be increased. These results set the stage for Specific Aim 3, where we will first use miR-21 antagomirs as well as a potential BMP activator identified in the HTS to increase BMPRII signaling in vivo, ie. in mice heterozygous for BMPRII. Second we will show that the above approach will prevent or reverse experimental PAH in BMPRII heterozygous mice (stimulated with hypoxia and Serotonin). Our ultimate goal is to initiate a clinical trial with the compound with the best efect/side-effect profile. The opportunity to modulate levels of relevant microRNAs and to identify a FDA approved drug that could arrest the progression or reverse PH by restoring normal BMP signaling would be a major breakthrough.